In Alien 3, when Ripley's asking Bishop if there was an alien on board, and his reply is, "It was with us all the way." I love that. I think it's because there's so much substance with regards to the alien just from that little statement. This creature that has plagued her, the threat, it's complete brutality, it's with her (and us) all the way. For me, the statement also echoes Ash's reply of "You can't" when asked how do they kill it. It's little touches like that in the earlier films that really reinforce the alien's terror.